1. Field of the Invention
The present invention relates to a process for making stable, high-viscosity organopolysiloxane emulsions and to an emulsion-polymerization process involving a simple, cost-effective, and faster organopolysiloxane emulsification and also subsequent organopolysiloxane polymerization. The process is directed to be simple and cost-effective and can be easily adapted for emulsion production of stable organopolysiloxane emulsions for diverse and beneficial end use applications. Importantly, the silicone emulsion produced by the process of the invention has average particle sizes (i.e. D50 value) in the range of up to 150 nanometers with a very narrow particle size distribution, and is highly stable and found to have advantageous, beneficial diverse uses in various end applications including personal care, textiles, rubber, paper, and other similar applications/uses.
2. Description of the Related Art
It is well known to provide organopolysiloxane emulsions of varying particle size to suit different end applications. Organopolysiloxane emulsions having small particle sizes prepared by an emulsion-polymerization process are generally preferred, which could provide a desired faster and simpler production, with a focus on emulsion stability and quicker organopolysiloxane polymerization during emulsification. Emulsion-polymerized products are known to be prepared by various methods. For example, JP-B 34-2041 discloses a polymerization process wherein a strong acid and strong base are used as a polymerization catalyst. U.S. Pat. No. 3,697,469 discloses ion-exchange resins as polymerization catalysts. U.S. Pat. Nos. 3,360,491; 3,697,469; 4,228,054; 5,726,270; 5,817,714; 5,895,794; 5,925,469; and 6,071,975 disclose polymerization using alkyl benzene sulphonic acid, alkyl naphthalene sulphonic acid, aliphatic sulphonic acid, silylalkyl sulphonic acid, aliphatically substituted diphenyl ether sulfonic acid or alkyl hydrogen sulphates as a catalyst. However, all these processes take longer time for polymerization and completion of the emulsion-making process. Most of the processes are also restricted only to cyclosiloxanes.
U.S. Pat. No. 6,245,852 discloses a process for preparation of organopolysiloxane emulsions having improved stability over a short time. The process comprises the steps of emulsifying and dispersing low molecular weight organopolysiloxane in water in the presence of at least one anionic surfactant selected from organic sulphonic acid and organic sulphates by using a high pressure homogenizer with a operating pressure range from 700 to 3,000 Kg/cm2 producing an initial emulsion having particle sizes of up to 300 nm, followed by allowing the emulsion to polymerize and subsequently neutralizing the emulsion.
As is clearly apparent from the disclosure in U.S. Pat. No. '852, the process necessarily involves the use of a very sophisticated and highly capital-intensive machine system for reduction of emulsion time in the emulsion polymerization process. Also, since the process uses a high-pressure system, the emulsion machine needs a complex control system for working safely in the production area.
Thus, while the process according to U.S. Pat. No. '852 is stated to reduce the time of emulsification by using a sophisticated high pressure homogenizer, the process does not seem to address the requirement for faster completion of the total emulsion process, including faster polymerization. An emulsion polymerization process usually consists of emulsification of organopolysiloxane and subsequent polymerization of the organopolysiloxane. Thus, faster emulsification on its own is not sufficient to complete an emulsion-polymerization process or make the process faster. Therefore, it is also important to make polymerization faster in emulsion-polymerization processes.
The above state of the art reveals the need to develop processes of making faster the total emulsion-polymerization process. Also, the reduction in the particle size which is found to be of relevance for a variety of end use/applications involving a faster emulsion-polymerization process is desirable for wide-scale commercial manufacturing and use of such emulsions for diverse applications.